(a) Field of the Invention
This invention relates to a view direction changing optical system adapted to endoscopes or particularly side view or rear view type hard endoscopes.
(b) Description of the Prior Art
In the case of any of straight view, oblique view, side view and rear view types, an endoscope is required to be designed so as to be housed in one pipe to make it air-tight (water-tight). Conventionally, in the straight view, oblique view and side view types, small optical systems are known. However, in the rear view type (in which the angle between the incident direction of light into an objective lens and the longitudinal direction of the endoscope is larger than 90 degrees), now there is no way to make the optical system small. The formation of the optical system which can be comparatively easily thought out by those skilled in the art to enable the rear view will be such formation as is shown in FIG. 1 or 2. However, in the case of such formation as is shown in FIGS. 1 and 2, in the case that the optical axis is to be bent once or twice, a lens L having a concave surface will have to be above the optical axis 0. Therefore, such concave lens can not be contained compactly in the pipe P in which the first optical member 1 and second optical member 2 can be compactly contained. Therefore, now there is no endoscope capable of rear viewing.